Selective Breeding
Overview: Selective breeding is when humans intervene with the natural reproductive cycle of organisms in order to breed plants and/or animals that express specific traits. Selective breeding is also known as artificial selection because humans actually pick out two organisms and breed them to produce a certain offspring. There are two main methods of selective breeding called the “breeder’s approach” and “controlled natural selection.” Breeder’s approach is when a breeder finds two organisms that have a high amount of a specific trait and then breeds them together in order to create an offspring with a high amount of the desired trait. Controlled natural selection is an approach which involves letting natural selection take its course, but within a controlled environment1. Overall, selective breeding is used to produce offspring that have a desired trait, such as breeding two different types of dogs to get a specific new type of dog. Plants can also be selectively bred in order to produce a specific type of plant, such as ones with increase crop yields, resistance to diseases, a high growth rate, and many others2. This genetic method is very well suited for producing offspring that express desired traits because professional breeders will only breed organisms that will produce the desired trait, and so the method is very efficient. Selective breeding has been taking place for a long time now, and continues to produce organisms, usually domesticated, that express a certain desired trait. Origins/Development: Selective breeding dates way back to Mesoamerica and the Romans and there is evidence that suggests an even earlier origin. In its early application, selective breeding was more focused on plants, particularly maize. In the 18th century, however, selective breeding was introduced to the scientific world by Robert Bakewell during the British Agricultural Revolution1. It was Bakewell that put selective breeding to use in order to produce offspring with desirable traits such as the Lincoln Longwool and the English Leicester, which are both sheep used primarily for wool production. He achieved these preferred offspring by breeding native stock that possessed traits such as large size, fine-bones, and long wool1. Horse and cattle were also animals that Bakewell selectively breed to produce a more desirable breed. It was Charles Darwin, however, that coined the term “selective breeding” as a part of his analysis of natural selection. He recorded that a lot of domesticated plants and animals were created by intentionally breeding certain plants and animals that possessed more desirable traits3. Method: Selective breeding can really be broken down into 4 simple steps: 1. Decide which characteristics (traits) are important. 2. Choose two parents that possess the desired characteristics. 3. Select the best offspring from the parents to breed next generation. 4. Repeat. This process can take some time depending on the plant/animal being bred, and this is why genetic engineering is slowly taking preference over selective breeding because it is much faster4. The only downfall to genetic engineering is that it sometimes produces harmful effects to the organisms and so it still has a few kinks to work out. There are two main categories of selective breeding, called: inbreeding and hybridization. Inbreeding is when two similar organisms are bred to create a similar offspring. Hybridization is when two dissimilar organisms are bred to create an offspring that possesses similar traits to both of the parent organisms. There are three different techniques that are utilized within animal breeding: line breeding, inbreeding, and outcrossing. Line breeding, similar to inbreeding, is when organisms are bred with their descendants or two cousins. So, essentially this process is breeding new offspring from the same line of descendants. Inbreeding is when an organism is bred with its daughters and granddaughters, etc. Outcrossing is when two unrelated organisms are cross-bred together in order to produce offspring1. Useful Examples: 1. Wheat: producing disease-resistant wheat by crossbreeding wheat plants with disease-resistant traits and wheat plants that have high-yield traits4. 2. Dairy Cattle: Increasing the yield of milk by breeding bulls with high-yield traits and cows with the best milk production4. 3. Cattle Breeds: ''Can produce cattle with different characteristics, such as cattle specifically for beef production or specifically for milk production4. 4. ''Dogs: Can breed two different types of dogs to achieve an offspring with desired traits such as certain physical characteristics or physical abilities such as hunting. Resources: 1. http://www.wikipedia.org 2. Selective Breeding by www.biologyonline.org 3. The Dire Wolf Project by The National American Alsatian Breeder's Association 4. New Genes For Old by bbc.co.uk 5. Artificial Selection: A Powerful Tool For Ecologists by Jeffrey Conner